Steels for hydrocracker vessels containing aluminum,columbium,molybdenum and nickel



United States Patent 3,475,164 STEELS FOR HY DROCRACKER VESSELS CON- TAINING ALUMINUM, COLUMBIUM, M0- LYBDENUM AND NICKEL Peter Paul Hydrean, Mahwah, N.J., assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 20, 1966, Ser. No. 587,963 Int. Cl. C22c 39/20, 37/10, 39/02 US. Cl. 75124 9 Claims ABSTRACT OF THE DISCLOSURE Steel which contains nickel, aluminum, molybdenum, columbium and low carbon offers a desirable combination of mechanical characteristics at elevated temperature and also resists temper embrittlement and hot hydrogen attack. Such properties in a steel are attractive in the fabrication of hydrocrackers.

As is generally known to those skilled in the art, hydrocracking involves a process of hydrogenation coupled with catalytic cracking wherein petroleum feed stock is treated with hydrogen gas under pressure (about 1000 to 2000 p.s.i.g.) at relatively high temperatures (600 F. to 850 F.) in the presence of a catalyst to produce gasoline or other high grade distillate. While the basic concept spans a period of nearly forty years, it has only been during the last decade that commercial exploitation of any consequence has been undertaken. But within this short period the impact industrially has been striking, a point perhaps best illustrated by a recent report which indicated that 38 gallons of gasoline were extracted from a 42-gallon barrel of crude using hydrocracking as opposed to but 21 gallons utilizing more conventional processing. This underscores the reasons for the expected expansion of hydrocracking.

In respect of the hydrocracker vessels per se, a common characteristic to all is their massiveness. Installed, a by no means unusual vessel is on the order of 100 feet in length, 10 feet in diameter (internal), and 7 inches thick, with a weight of one million pounds. As can be appreciated, the very magnitude of such dimensions, particularly wall thickness, not only gives rise to fabricating difficulties but renders transportion and erection (situs) particularly troublesome. Presently, these vessels are fabricated from a normalized and stress-relieved, low strength 2% chromium-1% molybdenum steel (ASTM, A387D). Now, it is the low strength thereof (60,000 to 80,000 p.s.i. ultimate) which is primarily responsible for the exceedingly thick walls necessary to resist the relatively high pressures encountered in operation. Accordingly, there is a more than definite commercial interest in utilizing higher strength steels whereby wall thickness, overall weight, etc., would be reduced, thereby minimizing the difiiculties now experienced.

But the problem is somewhat more complex than one of simply using a steel of high strength. By way of explanation, the hydrocracking reaction is conducted at elevated temperature, thus requiring a steel which not only retains high strength at elevated temperature but which also exhibits high temperature stability, i.e., the steel must perform without degradation of mechanical properties over long periods. This focuses emphasis on the fact that the steel must be tough and ductile at ambient and operating temperatures and resistant to temper embrittlement. It has been proposed to use the 2.%% chromium-1% molybdenum steel in the quenched and tempered (as opposed to the normalized and stress-relieved) condition, thereby increasing tensile strength; however, the steel would have a bainitic structure, a structure known to be particularly susceptible to temper embrittlement.

Further, as a consequence of hydrogenation, a steel, irrespective of its structural constitution, must manifest the capability of resisting hot hydrogen attack. If a steel is unable to cope with hot hydrogen, it thus becomes subject to blistering or fissuring even though cladded with austenitic stainless. In this regard the interior surface of hydrocracker vessel walls are, for the most part, cladded with austenitic stainless. Because of the very substantial wall thickness of vessels now in use, this must be accomplished by the weld overlay procedure, a costly and undesirable technique since it must be performed after fabrication of the vessel. But with appropriate high strength steels and accompanying thinner walls, the advantages of standard roll cladding could be realized.

It has now been discovered that a combination of desired mechanical characteristics, including high strength at ambient and elevated temperatures, toughness, ductility, resistance to both hot hydrogen attack and temper embrittlement, high temperature stability, etc., can be attained with steels of low carbon content and containing nickel, aluminum, molybdenum, and, advantageously, columbium, as described more fully herein.

It is an object of the invention to provide new and improved steels having characteristics which render the steels suitable for use in the fabrication of hydrocracker vessels.

Other objects and advantages will become apparent from the following description.

Generally speaking and in accordance with the present invention, alloys contemplated herein contain (in percent by weight) carbon in an amount up to less than 0.04%, about 5% to 10% nickel, about 0.7% to 1.2% aluminum, from 0.5% to 2% molybdenum, up to 1.5% chromium, up to 1% manganese, up to 1% silicon, up to 0.12% columbium, and most advantageously from 0.008% to 0.08% columbium, the balance being essentially iron. Constituents such as nitrogen, oxygen, sulfur and phosphorus should be maintained 'at low levels consistent with good commercial steelmaking practice. However, other elements may be present as follows: up to 5% cobalt, up to 1% or 2% copper, up to 0.01%, e.g., up to 0.005% boron, and up to 0.2% tantalum. Tungsten can be used in lieu of molybdenum on an atom for atom basis, two parts of tungsten for one part of molybdenum; however, molybdenum is appreciably more elfective than tungsten and is much preferred. Elements such as vanadium and titanium are quite unnecessary, although up to 0.2% of each can be tolerated. High amounts thereof detract from toughness.

In carrying the invention into practice, the carbon content of the steels should be less than 0.04% and it is beneficial that it not exceed 0.03%; otherwise, the risk is increased that nascent hydrogen evolved during the hydrocracking operation (and which permeates a stainless cladding) will combine or react with carbon present in the form of iron carbides. This reaction establishes the environment for methane gas to form at grain boundaries and other discontinuities. Eventually suflicient pressure may be built up from the trapped gas to cause fissuring or cracking. But as will be shown herein, relatively low carbon per se is not necessarily a complete penacea since other low carbon steels have been tested with resulting failure.

Nickel is required to confer adequate hardenability. Suitable nickel ranges are from 5% to 7% and, for optimum hardenability, 8% to 9.5%. Aluminum is a potent hardening and strengthening constituent, but excessive amounts thereof, e.g., 1.5%, should be avoided if the ability of the steels to absorb impact energy is not to be drastically impaired. Molybdenum confers strength and resistance to temper embrittlement and a particularly satisfactory range thereof is from 0.75% to 1.5%. Columbium, it has been found, imparts strength without adversely affecting toughness, provided that amounts appreciably above 0.12% are avoided. Too, it is deemed that columbium is effective in resisting fissuring, i.e., it is capable of combining with carbon to form carbides which are less readily attacked by hydrogen.

For the purpose of giving those skilled in the art a better understanding of the invention, the following description and illustrative data are given:

A series of alloys were prepared by either vacuum The compositions of the alloys are given in Table I, the age hardening Alloys 1. through 5 being within the invention whereas Alloys A, B and C are outside the scope thereof (Alloy A conforms to the aforementioned hydrocracker 2%% Cr1% Mo steel). In Table 11 room temperature (R.T.) and elevated temperature properties are reported. The Yield ,Strength (Y .S.) at 0.2% offset and Ultimate Tensile Strength (U.T.S.) are given in pounds per square inch (P.S.I.), the Elongation (EL) and Reduction in Area (R.A.) values in percent and the Charpy V-notch impact toughness (C.V.N.) determinations in foot-pounds (ft.-lbs.).

TABLE I Al, O Other, Fe percent percent percent percent percent percent 1. 02 11.9.. n.a. Bal. 0. 96 0. 008 n.a. Bel 1. 08 0. 008 11.9.. Bal. 1. 07 0. 06 0. 09 Bel. 1. 0. 08 0. 54 Bel. 0.54 Bal. 0. 03 0.38 Bal 0. 02 n.a. 0. 76 Bel.

n.a.=not added. =air melted. =added for deoxidation purposes. Bal.=ba1ance plus inpurities.

TABLE II Test Alloy Temp, Y.S U.T.S., EL, R. C.V.N. Number F. 11.5.! p.s.i. percent percent !t.-lbs.

R.T. 98, 800 111, 600 21 80 184 1 RT. 149, 900 154, 900 21 71 10. 800 105, 200 114, 300 22 75 R.T. 98, 100 113, 500 19 82. 5 181 2 R.T. 150, 500 155, 500 19. 5 70.8 17 800 107,800 115,000 23 75 A RT. 100, 000 124, 200 82. 5 224 3 R.T. 153, 400 167, 600 19 68. 5 47 B 800 114,700 129,700 20 75.0 C 800 125, 000 136, 700 20 71. 5 RIP. 140, 100 143, 500 21 76 116 4 B 650 113,100 118, 100 21 75 B 850 91, 200 101, 000 25 80. 8 RT. 160, 100 199, 200 16. 5 59. 5 5 D 650 145,900 179,000 18.5 65.0 D 850 132, 400 162, 200 17. 0 59. 8 Q & T RT. 108, 400 134, 000 18 63. 8 16 A Q & T 650 99, 600 149, 200 17 47. 2

Q, & T 850 88, 000 134, 600 19 49. 0 E RT. 82, 600 100, 100 27 72. 2 SO. 3 B E 650 67,200 ,200 23.5 59.5

E 850 54, 800 67, 500 23. 5 49. 0 F RT. 121, 950 136, 950 19. 5 68. 8 79. 0 C F 650 102, 000 116,200 17. 5 60. 0

Q & T=Quenched and Tempered.

induction or air melting processing. Ingots were forged and thereafter hot rolled to A-inch rounds or %-inch square bars (Alloy 5, Table I in form of Vz-inch plate), which, prior to testing were then given one or more of the following heat treatments:

Heat Treatment A:

(1) Heat treated at 1600 F. for 1 hour, air cooled. Heat Treatment B:

(1) Heat treated at 1600 F. for 1 hour, air cooled. (2) Heated to 1000 F. and held for 2 hours followed by air cooling. Heat Treatment C:

(1) Same as B except steels water quenched after heating to 1600 F. Heat Treatment D:

(1) Heat treated at 1600 F. for 1 hour, then fan cooled to simulate cooling rate of a water quenched 4-inch thick plate.

(2) Heated to 950 F., held for 3 hours, air cooled.

Heat Treatment E:

(1) Aged 1 hour at 1050 F. Heat Treatment F:

(1) Same as D except heated to 1050 F., held for 4 hours and air cooled.

With regard to the data in Table II, the alloys within the invention manifested satisfactory room and elevated temperature mechanical properties, a tensile strength of nearly 200,000 p.s.i. and an impact strength of 30 ft.-lbs. (Alloy 5) at room temperautre and a strength of over 160,000 p.s.i. at 850 F. being deemed quite satisfactory. It should be explained the reason for the low impact energy levels of Alloys 1 and 2 (Heat Treatment B) at 7 room temperautre stems from fact these alloys were low 000 p.s.i. could be obtained; however, the Charpy V Notch impact strength was quite low, to wit, 6-7 ft.-lbs.

Alloys 5, B and C were also tested to ascertain their behavior regarding long term stability, temper embrittlement and resistance to hydrogen under pressure. The results of this more discriminate and informative testing are set forth in Table III.

TABLE III Y.S., U.T.S., EL, C.V.N., Alloy Condition p.s.i. p.s.i. percent percent ft.-lo.

5 Before Exposure 160, 100 199, 200 16.5 59. 5 30 After 500 hrs. at 750 F. 15 54. 25 After 5,000 hrs. at 750 F 16. 59. 8 22 After 500 hrs. at 850 F 169, 200 200, 000 14 50. 0 24. 5 After 500 1118. at 750 F. and

1,000 p.s.i.g. H2 168, 800 198, 300 54. 0 25 After 500 hrs. at 850 F. and

1,000 p.s.i.g. H 169, 200 200,000 14. 5 50.0 24. 5

B Before Exposure 82, 600 100,100 27 72. 5 80. 3 After 5,000 hrs. at 650 F 81, 800 98, 000 24 72 48 After 5,000 hrs. at 850 F 85, 300 100, 000 25 69. 5 33 After 1,000 hrs. at 850 F. and

1,000 p.s.i.g. Hz 66, 300 76, 800 7 7 1 C Before Exposure 121, 950 136, 950 19. 5 68. 8 79. 0 After 5,000 hrs. at 750 F- 142, 750 155,750 18. 5 66. 0 22 After 5,000 hrs. at 850 F 131, 200 145, 000 16.5 57. 8 3

Whereas Alloy 5 behaved quite well, Table III, Alloys B and C performed poorly. Low carbon Alloy B manifested susceptibility to temper embrittlement and also was exceedingly prone to hydrogen attack. Examination revealed severe grain boundary attack. Similarly, Alloy C lost virtually all ability to absorb impact after prolonged exposure to 850 F.

A further compositional range suitable for hydrocracker applications is as follows: carbon up to 0.03%, 5% to 9.5% nickel, 0.75% to 1.2% aluminum, 0.75% to 1.5% molybdenum, 0.008% to 0.08% or 0.1% columbium, up to 1% chromium, up to 0.75% manganese, up to 0.5% silicon, and the balance essentially iron. A particularly satisfactory steel consists essentially of about 0.02% carbon, about 9% nickel, about 1% aluminum, about 0.9% molybdenum, about 0.06% to 0.1% columbium, about 0.5 manganese, about 0.2% silicon, with the balance being iron.

Although the present invention is specifically addressed to hydrocrackers, the subject steels can otherwise be used in sundry environments, particularly applications where steels affording both relatively high strength and good toughness are required. The steels can be produced and used in the form of plate, bar, rod, forgings, etc.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

I claim:

1. A novel alloy steel adapted for use in fabricating a hydrocracker vessel therefrom, said steel consisting essentially of less than 0.04% carbon, about 5% to 10% nickel, about 0.7% to 1.2% aluminum, from 0.5% to 2% molybdenum, columbium present up to 0.12%, up to 1.5 chromium, up to 1% manganese, up to 1% silicon, up to 5% cobalt, up to 2% copper, up to 2% tungsten, and the balance essentially iron.

2. A steel in accordance with claim 1 containing at least 0.008% columbium.

3. A hydrocracker vessel formed from the steel of claim 1.

4. A hydrocracker vessel formed from the steel of claim 2.

5. A steel in accordance with claim 1 in which the nickel content is from 5% to 7%.

6. A steel in accordance with claim 1 in which the nickel content is from 81% to 9.5

7. A steel in accordance With claim 1 and consisting essentially of carbon up to about 0.03%, 5% to 9.5% nickel, about 0.75 to 1.2% aluminum, about 0.75% to 1.5% molybdenum, from 0.008% to 0.08% columbium, up to 1% chromium, up to 0.75 manganese, up to 0.5% silicon, and the balance essentially iron.

8. A hydrocracker vessel formed from the steel of claim 7.

9. A steel in accordance with claim 7 consisting essentially of about 0.02% carbon, 9% nickel, about 1% aluminum, about 0.9% molybdenum, about 0.06% to 0.1% columbium, about 0.5% manganese and about 0.2% silicon.

References Cited UNITED STATES PATENTS 3,284,191 11/1966 Hydrean -124 3,262,823 7/1966 Sadowski.

3,303,023 2/ 1967 Dulis.

3,368,887 2/1968 Clark 75-124 X HYLAND BIZOT, Primary Examiner US. Cl. X.R. 

